A powerful technology for analyzing matter involves measuring the reflectance from or the transmission through the matter to be analyzed at narrow band wavelengths in the near infrared range known as NIR. To carry out such analysis, the matter is irradiated with NIR light and the amount of light transmitted through or reflected from the matter at narrow band wavelengths is measured and analyzed. Instruments for making such measurements are disclosed in U.S. Pat. Nos. 4,264,205 and 4,285,596 to Isaac J. Landa and U.S. Pat. No. 4,040,747 to Donald R. Webster. When the matter to be analyzed is in the form of bulk powder, the reflectivity of the powder can be measured by means of a probe immersed in the powder. Infrared light is transmitted to the probe by fiber optics and infrared light reflected from the powder to the probe is carried to a photodetecting analysis system. Normally, the restriction of the light to narrow band wavelengths is achieved by transmitting a narrow band wavelength of light to the powder and scanning the center frequency of the narrow band wavelength through the near infrared spectrum. Alternatively, a wide band of near infrared light could be transmitted to the probe and the received light could be subjected to separation into narrow band components. The use of the probe to analyze the powder in a manner as described above is not fully satisfactory because a substantial amount of the infrared light is specularly reflected from the powder and received by the probe. The specularly reflected light interferes with accurate analysis of the powder.